Interpretive Summary: The carrot psyllid is a serious insect pest of carrots in northern and central Europe, where it can cause up to 100% crop loss. This psyllid damages carrot by transmitting to the plant the new bacterium Liberibacter, recently found to severely affect potatoes and several other important crops in the United States. Researchers at USDA-ARS Wapato, in collaboration with scientists at the Norwegian Institute for Agricultural and Environmental Research in Norway, determined that the bacterium was widespread in several counties in southeastern and eastern Norway, where most of the carrot crops are grown. Information from this research will help carrot producers reduce damage caused by this pathogen to carrot crops by vigorously monitoring and controlling the carrot psyllid, its insect vector.

Technical Abstract:
The carrot psyllid Trioza apicalis Förster (Hemiptera: Triozidae) is a serious insect pest of carrot (Daucus carota L.) in northern Europe, where it can cause up to 100% crop loss. Although it was long believed that T. apicalis causes damage to carrot by injection of toxins into the plant, it was recently established that this psyllid is a vector of the recently discovered bacterium “Candidatus Liberibacter solanacearum”, which severely damages carrot crops. This bacterium is also known to severely affect solanaceous crops and is the causal agent of zebra chip, a new and economically important disease of potato in North and Central America and New Zealand. Symptoms in psyllid-affected carrots include leaf curling, yellowish and purplish discoloration of leaves, stunted growth of both leaves and roots, and proliferation of secondary roots. These plant symptoms resemble those caused by leafhopper-transmitted phytoplasmas and Spiroplasma citri in carrots. Using polymerase chain reaction (PCR) assays, a survey of “Ca. L. solanacearum” in carrot crops in Norway determined that the bacterium was widespread in several counties in southeastern and eastern Norway, where most of the carrot crops are grown. Liberibacter infection rate ranged from 33.3 to 100% in carrot plants and from 21.2 to 56.3% in T. apicalis. No phytoplasmas or spiroplasmas were detected in carrot or psyllid samples by PCR. Information from this research will help carrot producers reduce damage caused by “Ca. L. solanacearum” to carrot crops by vigorously monitoring and controlling T. apicalis, its insect vector.